The present invention relates to a suspension system for vehicles and more particularly to a suspension in which two similar hydraulic shock absorbers respectively connect different portions of the suspended part of the vehicle to respective non-suspended parts. In still greater particularity, each shock absorber is of the type which includes a cylinder delimited at its top by an annular cylinder head and at its bottom by a fixed valve-containing body. Inside the cylinder of each shock absorber there is slidably mounted a valve-containing piston which divides the cylinder into an upper chamber and a lower chamber and to which a rod extending through the upper cylinder head is rigidly fixed. Each shock absorber also includes a compensation chamber which communicates hydraulically with the lower chamber of the cylinder by way of the valve-containing body. This communication is controlled by automatic compression and compensation valves incorporated in the valve-containing body. The two shock absorbers are interconnected by hydraulic tubes such that, when the two shock absorbers are working in opposite directions, an extension of one causes an increase in resistance to compression of the other.
Suspensions of this general type are used to limit roll on heavy vehicles and on vehicles where the center of gravity is high. Examples of road vehicles of this kind are buses and large delivery vans. In these applications, the interconnected shock absorbers are associated with the opposite wheels of a common axle of the vehicle.
Another example of a vehicle where it is advantageous to use such a suspension is on a railway carriage. In this case the interconnected shock absorbers are arranged, on both sides of the carriage, between the suspended part and the non-suspended part of the carriage.
The systems used heretofore to limit the rolling action of a vehicle using shock absorbers are based on the principle of a direct crossed connection between the upper and lower chambers of each working cylinder of the two shock absorbers. A system of this kind is illustrated and described, for example, in the document IT-A-1,032,551.
In this known system, the oil in the shock absorber, which is compressed between the piston and the annular cylinder head or upper end during extension of one of the shock absorbers, is conveyed into the lower chamber between the piston and the compression valve of the other shock absorber which at the same time is being compressed. This oil flow opposes the compressive movement, thereby increasing the rolling resistance of the entire suspension.
However, this known system has certain shortcomings with regard to the tubes for connecting the shock absorbers which must be able to withstand high rates of flow under considerable pressure. Also, the tubes must be able to withstand radial deformation, so as not to introduce elasticity into the damping system. A further problem concerns the requirement for a special calibration procedure of the valves in order to avoid an imbalance in the oil flow under in all conditions.